Many elderly people now carry personal help buttons (PHBs) or personal emergency response systems (PERS) that they can activate if they need urgent assistance, such as when they fall. Automated fall detectors are also available that monitor the movements of the user and automatically trigger an alarm if a fall is detected.
These devices (i.e. PHBs, PERS and fall detectors) can initiate a landline call via a base unit located nearby to the user (i.e. typically in the user's home) to a dedicated call center when they are activated, and the personnel in the call center can talk to the user and arrange for assistance to be sent to the user in an emergency. As the user is a registered subscriber to the PHB/PERS service, their home location (or other location where the base station is found) will be known, and the emergency assistance can be directed to that location by the call center personnel.
However, systems are now available that make use of a mobile telephone or other mobile telecommunications-enabled device carried by the user to allow the PHB, PERS or fall detector device to initiate a call over a mobile telecommunications network to the call center. These devices are sometimes referred to as mobile PERS (MPERS) devices and can be used anywhere where there is cellular network coverage. As the typical users of these MPERS devices are elderly or those with some form of physical or mental impairment, it is important for the devices to be as simple to operate as possible. As a result, mobile telecommunications functionality is preferably integrated into a dedicated PHB or PERS pendant that is worn by the user and that typically only has a single activation button or a very small number of manual controls. On activation of the MPERS device, a call is automatically placed to the call center number preset in the device.
It is also desirable for these MPERS devices to be able to determine the location of the device (and thus the user) when an event such as a fall or the user pressing the PHB to request assistance occurs and to pass this location to the call center or emergency services so that the user can be easily located.
Currently, satellite positioning systems, such as GPS, are one of the most accurate location data sources available to portable or mobile electronic devices, such as an MPERS device. However, there are a number of drawbacks associated with satellite positioning systems. For example, it might not be possible to receive signals from the satellites when the device is indoors, under heavy foliage or in an ‘urban canyon’ (i.e. between a number of tall buildings), making it impossible to obtain a location measurement (sometimes referred to as a ‘fix’). Satellite positioning systems can also be prone to errors in the location measurement which can be due to a number of different reasons, including ‘multipathing’ where the signals from a satellite can reflect off of buildings before reaching the satellite positioning system receiver. These errors can cause the reported location to be some distance from the actual location, sometimes even as far as several city blocks. Another drawback with satellite positioning systems is that the receiver consumes a relatively large amount of power while making a location measurement.
Although the satellite positioning system receiver can be manually activated and deactivated by a user of the device to help reduce the power consumption, when some event occurs where it is useful to know the exact location of the MPERS device (for example if the user of the device is placing an emergency call and needs to provide their exact location, or the user of the device suffers a fall or other accident and the device is configured to automatically request assistance for the user), activating the satellite positioning system receiver and attempting a measurement is not without risk, as it might not be possible to get a measurement in the current location of the device.
Therefore, in such situations, it can be useful to make use of the last known location of the device obtained using the satellite positioning system receiver before the satellite signal was lost (this is sometimes referred to as ‘backtracking’ or ‘breadcrumbing’). To do this, the satellite positioning system receiver must either collect location measurements continuously (which means that the receiver will quickly drain the battery of the device), or a ‘breadcrumbing’ technique is used, in which the satellite positioning system receiver is selectively activated by the device to intermittently receive satellite positioning system signals and make location measurements. As the receiver is not continuously powered or active, there is some reduction in the power consumption of the device. If the receiver is unable to determine the location of the device when it is activated, the last acquired location measurement (breadcrumb) is used as an estimate of the current location of the device.
A further concern is that the device may be in a location in which coverage from the mobile telecommunications network is poor and which only permits data transfer at very low data rates, which prevents a large amount of location data being transmitted from the MPERS device to the call center or emergency services quickly. Therefore, the need to transmit large amounts of location data from the MPERS device should be minimized.
Therefore, there is a need to improve the existing breadcrumbing techniques to maximize the battery life and reduce the frequency with which the user has to recharge or replace the batteries, while maximizing the chance that the device can provide an accurate location or position measurement when required.